This invention relates generally to liquid drainage systems used on site for footings, open trenches, or nitrification fields used as discharge points for septic tanks, and more particularly to a novel flexible preassembled drainage line unit which is an improvement over the flexible preassembled drainage line units illustrated in FIGS. 2 and 3 of U.S. Pat. No. 5,015,123 (the “'123 patent”, owned by the assignee of this invention), the disclosure of which is incorporated herein by reference in its entirety.
The preassembled drainage line unit illustrated in FIG. 2 of the '123 patent constitutes loose aggregate in the form of lightweight materials such as polystyrene beads provided in surrounding relationship to a perforated conduit and bound thereto by a perforated sleeve member such as plastic netting. These units, used in combination with preassembled units illustrated in FIG. 3 of the '123 patent which do not include the perforated pipe, provide a storage chamber or area for example for effluent from a septic tank until it can be absorbed by the surrounding soil as illustrated in FIGS. 4b and 4c of the patent and replaces the conventional gravel drainage system illustrated in FIG. 1 of the patent. Drainage systems employing the preassembled drainage line units of the '123 patent represent a substantial improvement over prior conventional gravel systems for reasons set forth in the '123 patent and have enjoyed substantial commercial success.
While those preassembled drainage line units have enjoyed commercial success, in certain applications problems have presented themselves. For example depending on the type of fill soil placed on top of the preassembled units, solids such as sand or dirt may pass downwardly through the netting into the void area between adjacent aggregate, clogging that area and causing an undesirable reduction in liquid flow through the aggregate. In other applications it is sometimes desirable that the pre-assembled units which are normally very flexible along their length possess greater rigidity along that length and still in other applications it is sometimes beneficial to provide structure as part of those units which promotes the growth of microorganisms within the drainage units.
The improved drainage products of the invention as described hereinbelow have been developed to overcome the problems associated with the units described in the '123 patent and to fulfill the needs described above.